It is well known in the field of foundry work, to form hollow articles of intricate shape, by first forming a dissolvable core, forming a wax mould thereabout, and then inserting pins in the wax, so that their inner ends abut the core, and their outer ends protrude from the wax. A damp ceramic frit is then applied to the wax, thus covering the outer ends of the pins. The frit is dried so as to solidify it, and provide it with sufficient strength to hold the pins firmly. The wax is then melted and allowed to run from between the core and the frit, and molten metal is poured into the resulting space.
A machine which cuts the pins to a required length, and places them into wax covering a core, is described, illustrated and claimed in European patent 0072088, owned by the applicant for a patent for the present invention, as disclosed and claimed in this specification.
Experience gained during use of the machine, the subject of European Patent 0072088 in the production of hollow turbine blades, showed that the machine functioned perfectly, but the pins produced thereby generated unacceptable local stress loads into the surface of the casting. During solidifying of the metal, small, unavoidable relative movement occurs between the casting and the hardened frit, at a time insufficient for the pins to have been melted and absorbed by the cast metal. Stress in the form of tension was thus created in the blade surface at each place of contact with a pin, which required a dressing operation to remove it, some blades being scrapped as a result.
A first aspect of the present invention seeks to provide an improved core locating pin. Accordingly, a core locating pin which in operation spaces a core from a surrounding ceramic frit, by having one end buried in said frit, and the other end abutting said core, comprises a rod which includes an indentation intermediate its ends, said indentation being so positioned therein as to lie entirely within said frit, with one edge coinciding with the interior face thereof.
A further aspect of the present invention seeks to provide an improved core locating pin forming and fitting machine. Accordingly, a core locating pin forming and fitting machine comprises a cylindrical body containing a pressure actuated piston and rod, said rod having a first bore diametrically therethrough at a position adjacent its free end, which bore, in one position of said rod, and via a bore in the cylinder wall, receives pin wire from an external source, said rod having a second bore normal thereto and connecting said first bore with a space between the rod end and the end wall of the cylindrical body, which space contains a punch device which in operation passes through said second bore, and punches an indentation in pin wire when it is loaded into said first bore, prior to said pin wire, when in said first bore, being cut to form a pin of a desired length by movement of said piston and rod relative to said cylindrical body, to a position wherein said first bore is aligned with a further, pin ejection bore in the wall of the cylindrical body.